Method of preparing coating composition



UNHTED STATES PATENT QFFME METHOD OF PREPARING COATING COMPOSITION William F. May. Maywood, 111., assignor to American Can Company, New York, N. Y., a corporation of New Jersey No Drawing. Application March 19, 1942, Serial No. 435.427

1 Claim. (Cl. 26042) The present invention relates to a no-solvent also require that the inner surface of the can parcoating material for a metallic can body and ticularly at the sideseam be protected against has particular reference to a material which is a product coming into contact with the steel base a homogeneous mixture of two compatible resins metal of the can bodv. derived from hydrocarbon polymers, prepared by 5 An object of the present invention is the provimilling and without any solvents or softeners sion of a coating material consisting of a homoand producing a coating which requires no bakgeneous mixture of compatible hydrocarbon reing or drying heat after its application to the sins which are milled together to provide a. coatcan body surface, thus adapting it to the coating ing finally adaptable for forming a continuous of formed can bodies as well as to other pur- 'lining for all or a part of the can body inner sur= poses. face to which it is applied and which need not Sheet metal containers which are used for conbe baked or cured. taining foods are made usuall from tin plate Numerous other objects and advantages of the which provides a tin coated surface on both the invention will be apparent as it is better underoutside and the inside of the can. In manufacstood from the following description which is of turing the can body its side seam is formed usually a preferred embodiment thereof. with lock and lap sections which subsequently The coating material formula hereinafter given are soldered. In the bending of the metal incias an example of one embodiment of thepresent dent to the formation of the side seam, the tin invention shows a new use for compatible hydrosurface on the inside of the can often is broken carbon resins which when properly combined or otherwise damaged adJacent the seam area without the use of solvents or other softening so that certain food products react with the metal agents provide a surface covering material which base exposed by the disturbed tin lining and will possess the desired characteristic. cause corrosion. Such corrosion sometimes takes The coating or lining material of the present place at the side seam even when the tin sur- .5 invention consists of two compatible hydrocarbon face has been protected further by an interior resins which may be milled together and brought lining since during the seam forming operation to a coating viscosity without the use of any both tin and lining may be disturbed at the side other materials. Such mixture comprises a rubseam. ber-like, high molecular weight, polymer of iso- The inner surfaces of can bodies heretofore 80 butene and a clear water-white or prime-white have been stripe coated with protective linings viscous or solid cycloparaflln resin derived from and the vulnerable side seam area has been cova hydrogenated coumarone-indene type resin and ered by such a stripe coat. An example of this having a mel in p n range 0 from 145 degrees is shown in the W. E. Taylor United States Pat- C. to 155 degrees C. Preferably, one part of the ent No. 2,178,618. The coating material of the polybutene is combined with three parts of the present invention, to cite merely one example other resin. This percentage may be varied to of use, can be employed in a similar manner if provide for a coating material having. more or desired and is superior to the Taylor stripe coatless flexibility. ing for certain products in that it is prepared A linear polybutene also known as a rubberwithout any solvents and is applied to the seam 40 like, high molecular weight polymer of isobutene area in a heated condition, whereupon it ets imwhich is satisfactory for the present purpose is mediately without the need of a bake or any furmade by Advance Solvents and Chemical Corpother curing step. ration of New York city and is sold under the A great number of processed food products retrade name of "Vistanex Medium." A suitable quire processing heat of 212 degrees F. or lower. resin for the second part of the mixture is made The coating material of the present invention it the Neville Company of Pittsburgh, P a., and when applied to the inside surface of a can conis sold under the trade name of Nevillite No. 1." taining such food products will not be disturbed .Vistan'ex is the name given to a series of high by this relatively low processing heat. Obviously molecular weight hydrocarbon polymers whose such a temperature will not disturb the solder or physical consistency is governed largely by their other bonding medium at the side seam. molecular weight. Chemically Vistanex is The present invention contemplates the avoidconsidered'to consist of linear polymers with a ance of corrosion diillculties of cans for those negligible degreeofunsaturation. Vistanex Mefood products which require processing temperadium" is one of this series and is a tough, dry, tures not in excess of 212 degrees F. and which so elastic, rubbery resin, similar to whitecrepe rubher in appearance. "Vistanes" is chemically resistant to most acids, alkalies and salts, is odors less and nontoxic.

Chemically; "Nevillite No. 1" may be described as a cycloparaifin, or naphthene polymer. This cycloparafiin is derived from the hydrogenation of coumarone-indene type: resin. "Nevillite No. 1" contains no esters and is consequently unsaponifiable; its acid number is negligible (about .85) and its unsaturation as indicated by iodine number is quite low, the iodine number ranging from 30 to 45. Its compatibility is limited, but it is compatible with "Vista-nex" and it was discovered that it is compatible especially with Vistanex Medium for the specific objective of thepresent invention. It is permanently thermoplastic, waterwhite, tasteless and nontoxic.

In preparing a suitable mixture of Vistanex and Nevillite resins, for example, for the average stripe or other surface coating of cans suitable for products requiring a processing temperature not in excess of 212 degrees? the following procedure may be used. The desired quantity of Vistanex is put into an ordinary rubber mill with cold rolls and the Vistanex is worked for about one hour or until the resin is broken down so that a smooth sheet is obtained on the rolls.

The Nevillite resin in the meantime has been powdered and this now is added slowly to the milling Vistanex and it will require approximately one to two hours in which to add all of the Nevillite resin, the quantity used being substantially three times that of the Vistanex. A suitable milling action may be obtained during this procedure if the mill is maintained at a temperature of from 100 degrees F. to 140 degrees F.

After all of the Nevillite has been added better results may be obtained by raising the temperav ture of. the milling rollers to about 200 degrees F. and with this temperature the mixture is fur; ther milled for about one half hour. The resulting product may be allowed to cool and may be stored until its use.

aseasos In applying the stripe coating, for example, to

the side seam of a can body, it is merely necessary to heat the coating material until it becomes sufficiently plastic or liquid so that it can be brushed or fiowed onto the can surface to be covered. After application the film sets without the necessity of a baking or other curing step and thereafter provides a satisfactory coating for the body wall. After the product has been sealed in a can having such a lining a subsequent processing temperature 01.212 degrees 1''. or less will not afiect the coated film.

It is thought that the invention and many of its attendant advantages will be understood from the foregoing description, and it will be apparent that various changes may be made in the matter of the ingredients, their identity and their proportions without departing from the spirit and scope of the invention or sacrificing all of its material advantages. the form hereinbefore described being merely a preferred embodiment thereof.

I claim:

The method of preparing a coating composition which has high chemical and corrosion resistance for application to the surfaces of sheet metal containers, which method comprises the steps of milling together, without the use of solvents or softeners, three parts by weight of a water white, unsaponifiable and substantially nonacidic cycloparafiine resin derived from the hydrogenation of indene andcoumarone resins and having a melting point range of from 145 degrees centigrade to 155 degrees centigrade and one part by weight of a compatible, rubber-like, high molecular weight polymer of isobutene, saidmilling being accomplished at a temperature of from degrees Fahrenheit to 200 degrees Fahrenheit and for a time sufiicient to obtain a homogeneous mixture of high viscosity, then heating said mixture to lower its viscosity to a point where it may be applied to said surfaces in heated condition.

' WHLIAM F. MAY. 

